Optical anisotropy is known in the art for dopes (or solutions) of synthetic polyamides, e.g., the dopes of Kwolek U.S. Pat. No. 3,671,542. Liquid crystal behavior is reported for polyolefin melts in, e.g., SPE Transactions, January, 1965, pp. 15-21 and in Kolloid-Zeitschrift and Zeitschrift fur Polymere, 250, 27-37 (1972). Optical anisotropy has not been reported for melts of polyesters before this invention.
Poly(ethylene terephthalate), the polyester most commonly used for commercial fiber production, is melt-spun and then drawn to induce orientation and increase its strength. The provision of novel polyesters which can be melt spun directly into useful oriented fibers without the need for afterdrawing is a desirable objective.